(1) Field of the Invention
The present invention relates to a network system, network device, and network belonging judgment method that are capable of judging whether a plurality of network-connected devices belong to the same home network.
(2) Description of the Related Art
As the number of information devices used at home is increased, a home network system is commercialized. In the home network system, a LAN (Local Area Network) to which various devices are connected and mutually exchange content is established. When information devices use copyright-protected digital content, illegal duplication or use of such content is prohibited such as posting of content on the Internet to be accessed or acquired by the general public. Meanwhile, there is a proposal in which digital content is permitted to be copied and to be distributed into a device inserted in a home network within the scope of private use, which is a limited scope of the home network and the like, from a perspective of flexible management of digital content. It is also conceivable that the devices belonging to the same home network may be entitled to receive specific services in addition to the use of digital content.
To establish and properly manage such a home network as described above, it is necessary to determine the network to which various information devices belong. Further, when a plurality of devices exchange content, it is necessary to accurately judge whether the devices belong to the same home network. Methods for defining the network belonging of each device are described below.
A first method formulates a definition by using an IP packet TTL (Time To Live) value in an IP network that is disclosed by Non-patent Document 1 (RFC791, Internet Protocol, J. Postel, September 1981). For example, the TTL value is set to 1 to limit content distribution to a range that is not beyond a router. More specifically, this method defines a home network as a single physical network, and judges that devices physically connected to the same physical network belong to the home network.
A second method uses a group management server that is disclosed by Patent Document 1 (Japanese Patent Laid-open No. 2005-301633). This method defines devices registered in the group management server as devices that belong to the same home network. Content is permitted to be privately used within the same home network. Further, the content can be distributed and played back under separately stipulated content playback permission conditions or the like.